This invention concerns methods and systems for reading holographically recorded data.
Researchers have designed holographic data recording systems that potentially could provide commercially interesting recording densities and rates. Examples of such systems are those disclosed in U.S. Pat. Nos. 5,978,112 and 5,671,073 (both Psaltis et al.).
The present invention includes a method of generating a position error signal in a holographically imaged data recording system. This method comprises using an optical imaging system to image a plurality of holographically recorded pixels forming a data page, wherein each holographically recorded pixel is imaged onto an array of at least two adjacent camera pixels. The output signals from the arrays of camera pixels are used to calculate a position error signal.
The present invention also includes a method of generating a holographic data signal in a holographically imaged data recording system. The optical imaging system operates as set forth above. The output signals from the arrays of camera pixels are used to calculate the holographic data signal.
In one embodiment, the step of using an optical imaging system to image a plurality of holographically recorded pixels comprises choosing an integer ratio of center-to-center spacing between adjacent holographically recorded pixels to center-to-center spacing between adjacent camera pixels which is greater than one. The step of using an optical imaging system to image a plurality of holographically recorded pixels may comprise magnifying an image of a holographically recorded pixel by a factor greater than one.
Each array may be comprised of Mxc3x97N adjacent camera pixels, with each of M and N being at least two, e.g., 2xc3x972.
The position error signal may be calculated by a multidetector technique based on signals representative of motion in a first direction and signals representative of motion in a second direction. The first and second direction are different, e.g., they are orthogonal to each other.
The present invention also includes generating a translational position error signal. Each array of adjacent camera pixels contributes individually to the generation of the translational position error signal. Each array is comprised of at least four regions A-D: top left A, top right B, bottom left C, and bottom right D. A vertical position error signal is generated by calculating the difference between the sum of (A+B) and the sum of (C+D) for all of the arrays. A horizontal position error signal is generated by calculating the difference of the sum of (A+C) and the sum of (B+D) for all of the arrays.
The present invention also includes generating a rotational position error signal based on vertical and horizontal position error signals calculated for at least one of two halves of the data page.
The position error signals may be used to control relative positioning of a recording medium and the optical imaging array. The position error signals may also be used to control relative positioning of the optical imaging system and the plurality of camera pixels. Control of relative positioning may be accomplished by using a piezomirror to retarget the holographically recorded pixels onto respective centers of the arrays.
The optical imaging system may be used to steer the holographic data page to reduce the position error signal. This steering may be accomplished with a piezomirror.
The present invention also includes a system for generating a position error signal in a holographically imaged data recording system. The system comprises an optical imaging subsystem and a calculating subsystem for implementing the steps described above.